HTLV-1 is the etiological agent of adult T-cell leukemia lymphoma (ATLL). ATLL cells are characterized by constitutive NF?B activation, a key feature of other lymphomas, myeloma, and solid tumors. The Tax oncoprotein is the key viral determinant for NF?B activation. Our previous studies showed that the classical and especially, the alternative NF?B pathways were critical in conferring resistance to apoptosis. The current study will use innovative, physiological lymphoma models to define the role in tumorigenesis of each NF?B pathway and identify the key NF?B target gene responsible for these effects. Aim 1. Which NF?B pathway is critical for HTLV tumorigenesis in humanized mice? In this study, a new humanized mouse model is used for HTLV-1 infection and lymphoma development. We will use viral variants expressing Tax mutants with defects in activating the alternative NF?B pathway or both NF?B pathways, in order to define their role in disease pathogenesis. A novel high-throughput viral integration assay is used to monitor clonality of infected cells over the course o these experiments. Aim 2. Which NF?B targets are required for maintenance and progression of Tax transgenic tumors? In this study, a new inducible Tax transgenic mouse model of lymphoma is utilized to assess the role of specific NF?B target genes in tumor progression using microarray analysis. Aim 3. Which NF?B target genes are critical for HTLV transformation? In this study, shRNAs to NF?B1 (p105) and NF?B2 (p100) are used to assess each individual pathway. HTLV-1 transformed cells expressing one of both of these shRNAs will be subjected to microarray analysis to determine which pathway is responsible for activation of specific target genes. Moreover, their contribution of select NF?B target genes to resistance to apoptosis will be assessed. It is expected that the information these physiologically relevant mouse models will identify key target genes that may be inhibited in therapeutic trials of ATLL or other lymphomas.